The invention relates to a self-crosslinking coating system based on fluorine containing polycondensates, to a method for coating substrates with this coating composition, and to coated substrates thereby obtainable.
Thin, in many cases almost monomolecular, layers and impregnations of silanes and siloxanes containing perfluorinated side groups are used in order to give the surface of substrates water and oil repellency. However, the impregnations or layers, a few nanometers thick, do not provide the substrate surface with durable protection in the face of mechanical or chemical attack.
EP 0 587 667 (corresponding to DE 41 18 184) describes durable coating compositions based on polycondensates of one or more hydrolysable compounds M from main groups III to V and transition groups II to IV of the periodic table of the elements, at least some of these compounds being hydrolysable compounds containing perfluorinated side groups, especially hydrolysable silanes containing perfluorinated groups. These coating compositions can be cured but it is necessary to carry out crosslinking on the substrate by means of photochemical polymerization or of thermal polymerization at a temperature of at least 50xc2x0 C. As a result, their use is technically complex, since appropriate curing equipment is required. For large-surface-area applications in particular, such as on the facades of buildings, for example, this represents a considerable restriction.
It is an object of the present invention to provide a method for coating substrates which provides coatings having antistick properties without a special curing step and without specific curing equipment. These coatings should nevertheless be scratch resistant and durable with respect, for example, to chemical or mechanical attack. It is further intended that the coating material should be provided in an easy-to-handle and storage-stable form. This object is achieved in accordance with the invention by a method for coating a substrate by preparing a self-crosslinking coating composition based on
a) at least one hydrolysable silane containing at least one nonhydrolysable substituent, the silane containing one or more electrophilic groups X on at least one nonhydrolysable substituent,
b) at least one hydrolysable silane containing at least one nonhydrolysable substituent, the silane containing one or more nucleophilic groups Y on at least one nonhydrolysable substituent, and
c) at least one hydrolysable silane containing at least one nonhydrolysable carbonic group having on average from 2 to 30 fluorine atoms attached to one or more aliphatic carbon atoms separated by at least two atoms from the silicon atom,
the silanes (a), (b) and/or (c) having undergone prior condensation if desired and it being possible either for the silanes (a) to be replaced in whole or in part by organic compounds containing at least two groups X or for the silanes (b) to be replaced in whole or in part by organic compounds containing at least two groups Y,
applying it to a substrate and curing it at ambient temperature (below 40xc2x0 C.) to form a coating.
The coating composition used in the method of the invention may be obtained, for example, in the form of an easy-to-handle, storage-stable two-component coating system. This two-component coating system is characterized by
a component (A) comprising at least onexe2x80x94optionally precondensedxe2x80x94hydrolysable silane (a) containing at least one nonhydrolysable substituent, the silane (a) having one or more electrophilic groups X on at least one nonhydrolysable substituent, and
a component (B) comprising at least onexe2x80x94optionally precondensedxe2x80x94hydrolysable silane (b) containing at least one nonhydrolysable substituent, the silane (b) containing one or more nucleophilic groups Y on at least one nonhydrolysable substituent,
it being possible either for the silanes (a) to be replaced in whole or in part by organic compounds containing at least two groups X or for the silanes (b) to be replaced in whole or in part by organic
compounds containing at least two groups Y, and component (A) and/or (B) further comprising a hydrolysable silane (c) containing at least one nonhydrolysable carbonic group having on average 2 to 30 fluorine atoms attached to one or more aliphatic carbon atoms separated by at least two atoms from the silicon atom.
In one specific embodiment the coating composition of the invention further comprises nanoscale inorganic particulate solids which may have been surface modified.
Specific examples of the electrophilic group X are the epoxide, anhydride, acid halide and isocyanate groups.
Specific examples of the nucleophilic group Y are the amino group and the hydroxyl group.
Pairings which have proven to be particularly suitable for ambient temperature self-crosslinking include epoxy/amino and isocyanate/hydroxyl.
In accordance with the invention, self-curing, highly scratch-resistant coatings of low surface energy are obtained which adhere particularly well to the coated substrate without the need for a special curing step. The resulting coatings possess excellent antistick and easy-to-clean properties.
To prepare the coating composition the method of the invention uses as component a) at least one hydrolysable silane containing at least one nonhydrolysable substituent, the silane containing one or more electrophilic groups X on at least one nonhydrolysable substituent.
This component a) comprises a silicon compound possessing 1 to 3, preferably 2 or 3, with particular preference 3, hydrolysable radicals and 1, 2 or 3, preferably 1 or 2, especially one, nonhydrolysable radical(s). At least one of the nonhydrolysable radicals possesses at least one electrophilic group X.
Examples of hydrolysable groups, which may be identical to or different from one another, are hydrogen, halogen (F, Cl, Br or I, especially Cl and Br), alkoxy (e.g. C1-6 alkoxy, especially C1-4 alkoxy, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy), aryloxy (preferably C6-10 aryloxy, such as phenoxy), acyloxy (e.g. C1-6 acyloxy, especially C1-4 acyloxy, such as acetoxy or propionyloxy) and alkylcarbonyl (preferably C2-7 alkylcarbonyl, such as acetyl). Preferred hydrolysable radicals are halogen, alkoxy groups and acyloxy groups. Particularly preferred hydrolysable radicals are alkoxy groups, especially methoxy and ethoxy.
Examples of nonhydrolysable radicals containing no group X are alkyl (preferably C1-8 alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl and tert-butyl, pentyl, hexyl, octyl or cyclohexyl), alkenyl (preferably C2-6 alkenyl, such as vinyl, 1-propenyl, 2-propenyl and butenyl), alkynyl (preferably C2-6 alkynyl, such as acetylenyl and propargyl) and aryl (preferably C6-10 aryl, such as phenyl and naphthyl). The radicals may if desired contain one or more customary substituents, such as halogen or alkoxy, or functional groups not included among electrophilic groups X, examples being (meth)acryloyl groups and (meth)acryloyloxy groups.
Suitable electrophilic groups X are known to the person skilled in the art. Preferred examples include epoxy, anhydride, acid halide and isocyanate groups. Where two or more electrophilic groups X are present in the silane or where different silanes containing electrophilic groups X are used, X may have the same meaning or a different meaning.
Examples of nonhydrolysable radicals containing an epoxy group are in particular those which possess a glycidyl or glycidyloxy group. Specific examples of silanes of component a) which contain an epoxy group and can be used in accordance with the invention can be found, for example, in EP 0 195 493, whose entire disclosure is incorporated into the present specification by reference.
The nonhydrolysable radicals containing acid halide groups or acid anhydride groups X may, for example, be radicals deriving from carboxylic anhydrides or carbonyl halides. The halides in question may be the acid chloride, bromide or iodide, the acid chlorides being preferred. They may be anhydrides or halides of straight-chain or branched, aliphatic, cycloaliphatic or aromatic carboxylic acids, e.g. anhydrides and halides of (C1-8 alkyl)carboxylic acids, such as acetic acid, propionic acid, butyric acid and malonic acid, (C2-8 alkenyl)carboxylic acids, such as maleic acid, or (C6-25 aryl)carboxylic acids, such as phthalic acid. Specific examples are propionyl chloride, acetyl chloride, sulphonyl chloride, succinic anhydride, maleic anhydride, phthalic anhydride and acetic anhydride.
The electrophilic group X may be attached directly to the silane, but is preferably attached to the silane via a linking group. Further and specific examples of hydrolysable and nonhydrolysable groups and of silanes which can be used are set out hereinbelow.
Hydrolysable silanes particularly preferred in accordance with the invention and containing an electrophilic group X are those of the general formula (I):
Z3SiRxe2x80x83xe2x80x83(I) 
in which the radicals Z, identical to or different from one another (preferably identical), stand for a hydrolysable group and are, for example, a halogen (F, Cl, Br and I, especially Cl and Br), alkoxy (e.g. C1-6 alkoxy, especially C1-4 alkoxy, such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy and tert-butoxy), aryloxy (especially C6-10 aryloxy, e.g. phenoxy), acyloxy (e.g. C1-6 acyloxy, especially C1-4 acyloxy, such as acetoxy and propionyloxy) and alkylcarbonyl (e.g. acetyl), and R is a nonhydrolysable group containing at least one electrophilic group X. Particularly preferred hydrolysable groups Z are C1-4 alkoxy and especially methoxy and ethoxy.
The nonhydrolysable group R may be, for example, a group Rxe2x80x3X, in which X is the electrophilic group and Rxe2x80x3 is a bridging group which connects the group X to the silicon. The group Rxe2x80x3 may be an alkylene, alkenylene or arylene bridging group, which may be interrupted by oxygen groups or xe2x80x94NHxe2x80x94 groups. The bridging groups mentioned derive, for example, from alkyl radicals (preferably C1-20 alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl and tert-butyl, pentyl, hexyl, octyl or cyclohexyl), alkenyl radicals (preferably C2-6 alkenyl, such as vinyl, 1-propenyl, 2-propenyl and butenyl) and aryl radicals (preferably C6-10 aryl, such as phenyl and naphthyl). The radicals may if desired contain one or more customary substituents, such as halogen or alkoxy. The group X may be an epoxy, acid anhydride, acid halide or isocyanate group. The epoxy group is preferred. It is of course also possible for more than one electrophilic group X, identical or different, to be attached to the bridging group Rxe2x80x3.
A preferred nonhydrolysable radical R containing an epoxy group is a glycidyl-, or glycidyloxy-(C1-20) alkylene radical. Specific examples thereof include in particular xcex2-glycidyloxyethyl, xcex3-glycidyloxypropyl, 67 -glycidyloxybutyl, xcex5-glycidyloxypentyl, xcfx89-glycidyloxyhexyl, and 2-(3,4-epoxycyclohexyl)ethyl. Owing to their ready availability, xcex3-glycidyloxypropyltrimethoxysilane (referred to for short as GPTS hereinbelow) and xcex3-glycidyloxypropyltriethoxysilane (referred to for short below as GPTES) are used with particular preference in accordance with the invention.
Examples of suitable isocyanatosilanes are 3-isocyanatopropyltriethoxysilane and 3-isocyanato-propyldimethylchlorosilane. Examples of suitable silanes containing an acid anhydride group are 
The number and nature of the hydrolysable groups and of the nonhydrolysable groups for the hydrolysable silanes containing a nucleophilic group Y correspond to those indicated above for the hydrolysable groups containing an electrophilic group X. Mutatis mutandis, reference may therefore be made to the above explanations.
Examples of nucleophilic groups Y are amino groups and the OH groups. Examples of nonhydrolysable radicals containing amine groups derive, for example, from primary, secondary or tertiary amines. The group may be, for example, an xe2x80x94NH2, xe2x80x94NHR2 or xe2x80x94NR22, where R2 can be a group, for example, that was mentioned above for R.
Preferred silanes containing a nucleophilic group are those of the general formula (II):
Z3SiRxe2x80x2xe2x80x83xe2x80x83(II) 
in which the radicals Z are defined as in the case of the general formula (I) above and Rxe2x80x2 stands for a nonhydrolysable, Si-bonded radical which contains at least one nucleophilic group Y. The nonhydrolysable group Rxe2x80x2 may, for example, be a group Rxe2x80x3Y, where Y is the functional group and Rxe2x80x3 is a bridging group which connects the group Y to the silicon. Rxe2x80x3 is defined as above in the case of the general formula (I). Y is, for example, an amino group or a hydroxyl group. It is of course also possible for more than one nucleophilic group Y, identical or different, to be attached to the bridging group Rxe2x80x3.
Specific examples of such silanes containing an amino group are 3-aminopropyltrimethoxysilane (APTS), 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, and N-[Nxe2x80x2-(2xe2x80x2-aminoethyl)-2-aminoethyl]-3-aminopropyltrimethoxysilane. A specific example of the silane containing hydroxyl group is hydroxymethyltriethoxysilane. Specific examples of silanes containing amino group and hydroxyl group are bis(hydroxyethyl)-3-aminopropyltriethoxysilane and N-hydroxyethyl-N-methylaminopropyltriethoxysilane.
The molar ratio of the electrophilic groups X to the nucleophilic groups Y in the coating composition of the invention is preferably in the range from 5:1 to 1:1, more preferably from 3:1 to 2:1.
Either the hydrolysable silane compounds containing the electrophilic group X can be replaced in whole or in part by organic compounds containing at least two electrophilic groups X or the hydrolysable silane compounds containing the nucleophilic group Y can be replaced in whole or in part by organic compounds containing at least two electrophilic groups Y. The groups X or Y that are present in the organic compounds are the same groups specified above in connection with the corresponding hydrolysable silane compounds. It is not possible for both hydrolysable silane compounds to be completely replaced by corresponding organic compounds.
Where an organic compound is used, the electrophilic or nucleophilic groups it contains are to be taken into account when setting the preferred molar ratio between component a) and component b); in other words, in that case the preferred molar ratio of component a) to component b) is based on the molar amount of electrophilic group X present to the molar amount of nucleophilic group Y.
The aforementioned organic compounds may comprise organic monomers, oligomers or polymers containing at least two electrophilic or nucleophilic groups, or mixtures thereof. Use may be made of any compound which is known from the prior art and is suitable for these purposes. The compounds in question comprise, for example, aliphatic, cycloaliphatic or aromatic compounds.
Specific examples of organic compounds containing at least two epoxide groups are 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, bis(3,4-epoxycyclohexyl) adipate, 1,4-butanediol glycidyl ether, cyclohexanedimethanol diglycidyl ether, glycerol triglycidyl ether, neopentyl glycol diglycidyl ether, pentaerythritol polyglycidyl ether, 2-ethylhexyl glycidyl ether, 1,6-hexanediol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, epoxy resins based on bisphenol A, epoxy resins based on bisphenol F, and epoxy resins based on bisphenol A/F.
Specific examples of organic compounds containing at least two amino groups are 1,3-diaminopentane, 1,5-diamino-2-methylpentane, 1,4-diaminocyclohexane, 1,6-diaminohexane, diethylenediamine, triethylenetetramine or isophoronediamine. Specific examples of organic compounds containing at least two acid chloride groups are malonyl dichloride, succinyl chloride and adipyl dichloride. It is of course also possible to use organic compounds which carry different electrophilic or different nucleophilic groups.
The coating composition used in the method of the invention further comprises at least one hydrolysable silane (c) containing at least one nonhydrolysable carbonic group having on average from 2 to 30 fluorine atoms attached to one or more aliphatic carbon atoms separated by at least two atoms from the silicon atom. For simplification, these silanes are sometimes referred to below as fluorosilanes.
The number and nature of the hydrolysable groups and of the nonhydrolysable groups for the hydrolysable silanes containing a fluorinated group correspond, apart from the nonhydrolysable fluorinated group, to those specified above for the hydrolysable groups containing an electrophilic or nucleophilic group. To that extent, reference may be made, mutatis mutandis, to the explanations above. Specific examples of fluorosilanes which can be used in accordance with the invention can be taken from EP 0 587 667, hereby incorporated by reference.
The nonhydrolysable group containing F substituents Rxe2x80x2xe2x80x3 in the fluorosilane contains on average from 2 to 30, preferably from 5 to 30, fluorine atoms attached to one or more aliphatic (including cycloaliphatic) carbon atoms separated by at least two atoms from the silicon. The groups Rxe2x80x2xe2x80x3 contain preferably on average from 5 to 25 and in particular from 8 to 18 fluorine atoms attached to aliphatic carbon atoms, not counting those fluorine atoms which may be attached otherwise, for example to aromatic carbon atoms (in the case of C6F4, for example). The fluoric group Rxe2x80x2xe2x80x3 may also comprise a chelate ligand. It is also possible for one or more fluorine atoms to be located on a carbon atom which is the starting point for a double or triple bond. Since the group Rxe2x80x2xe2x80x3 is required to contain on average only 2 corresponding fluorine atoms, it is also possible to use groups Rxe2x80x2xe2x80x3 which possess only 1 fluorine atom, provided there are at the same time sufficient groups Rxe2x80x2xe2x80x3 present containing more than 2 fluorine atoms.
Preferred silanes containing a fluorinated group are those of the general formula (III):
Z3SiRxe2x80x2xe2x80x3xe2x80x83xe2x80x83(III) 
in which the radicals Z are defined as above in the case of the general formula (I) and Rxe2x80x2xe2x80x3 is, for example, a group as defined above or a group set out below.
Specific examples of fluorosilanes are C2F5xe2x80x94CH2CH2xe2x80x94SiZ3, n-C6F13xe2x80x94CH2CH2xe2x80x94SiZ3, n-C8F17xe2x80x94CH2CH2xe2x80x94SiZ3, n-C10F21xe2x80x94CH2CH2xe2x80x94SiZ3 (where Zxe2x95x90OCH3, OC2H5 or Cl); i-C3F7Oxe2x80x94CH2CH2CH2xe2x80x94SiCl2(CH3), n-C6F13xe2x80x94CH2CH2xe2x80x94SiCl2(CH3) and n-C6F13xe2x80x94CH2CH2xe2x80x94SiCl(CH3)2 
The fluorosilane (c) is used, for example, in an amount of from 0.005 to 0.05 mol per mole of component (a). Preferred amounts are in the range from 0.005 to 0.03 and in particular from 0.008 to 0.02 mol per mole of component (a).
The nanoscale particulate solids (d) comprise particles having an average size (average particle diameter) of not more than 1000 nm, preferably not more than 200 nm, more preferably not more than 100 nm, and in particular not more than 70 nm. Particularly preferred particle sizes are in the range from 1 to 100 nm, preferably from 2 to 50 nm and with particular preference from 5 to 40 nm.
The nanoscale (inorganic) particulate solids may be composed of any desired materials but are preferably composed of metals and in particular of metal compounds such as, for example, (optionally hydrated) oxides such as ZnO, CdO, SiO2, TiO2, ZrO2, CeO2, SnO2, Al2O3, In2O3, La2O3, Fe2O3, Cu2O, Ta2O5, Nb2O5, V2O5, MoO3 or WO3; chalcogenides such as, for example, sulphides (e.g. CdS, ZnS, PbS and Ag2S), selenides (e.g. GaSe, CdSe and ZnSe) and tellurides (e.g. ZnTe or CdTe), halides such as AgCl, AgBr, AgI, CuCl, CuBr, CdI2 and PbI2; carbides such as CdC2 or SiC; arsenides such as AlAs, GaAs and GeAs; antimonides such as InSb; nitrides such as BN, AlN, Si3N4 and Ti3N4; phosphides such as GaP, InP, Zn3P2 and Cd3P2; phosphates, silicates, zirconates, aluminates, stannates and the corresponding mixed oxides (e.g. indium tin oxides (ITO) and those with perovskite structure such as BaTiO3 and PbTiO3).
The nanoscale inorganic particulate solids used preferably comprise an oxide or oxide hydrate of Si or Al and also transition metals, preferably Ti, Zr and Ce, and mixtures thereof. Examples of such are nanoscale particles of SiO2, TiO2, ZrO2, ZnO, SnO2 and Al2O3 (in all modifications, especially as boehmite, AlO(OH)) and also mixtures thereof It is particularly preferred to use nanoscale SiO2 particles. For this purpose it is also possible, for example, to use commercial silica products, e.g. silica sols, such as the Levasil(copyright) silica sols from Bayer AG, or pyrogenic silicas, such as the Aerosil(copyright) products from Degussa. The particulate materials are available commercially in the form of powders and sols.
The nanoscale particulate solids may be used in this form or in the form of surface-modified particles. Nanoscale inorganic particulate solids provided with organic surface groups may be prepared in principle by two different routes: firstly by surface modification of pre-manufactured nanoscale inorganic particulate solids, and secondly by preparing the inorganic nanoscale particulate solids using one or more compounds that are suitable for surface modification.
Where surface modification of pre-manufactured nanoscale particles is carried out, compounds suitable for this purpose are all (preferably low molecular mass) compounds which possess one or more groups which are able to react or at least interact with (functional) groups (such as OH groups in the case of oxides, for example) present on the surface of the nanoscale particulate solids. Accordingly, the corresponding compounds may, for example, form both covalent and ionic (saltlike) or coordinative (complex) bonds to the surface of the nanoscale particulate solids, while pure interactions that may be mentioned include, by way of example, dipolexe2x80x94dipole interactions, hydrogen bonding and van der Waals interactions. Preference is given to the formation of covalent and/or coordinative bonds. Specific examples of organic compounds which can be used for surface modification of the nanoscale inorganic particulate solids include, for example, carboxylic acids, xcex2-dicarbonyl compounds (for example xcex2-diketones or xcex2-carbonylcarboxylic acids), alcohols, amines, epoxides and the like.
With particular preference in accordance with the invention, and especially in the case of oxide particles, surface modification is carried out using hydrolytically condensable silanes containing at least (and preferably) one nonhydrolysable radical. Examples of compounds suitable for this purpose are the aforementioned hydrolysable silanes of components a) to c). Where, for example, at least some of the hydrolysable silanes of components a) and/or b) are used for surface modification of the nanoscale inorganic particulate solids, and these surface-modified particles are used for the coating composition, the resulting coatings are extremely advantageous (scratch resistance). Alternatively, the fluorosilanes may be used for surface modification. By using particulate solids with surface modification of this kind in the coating composition it is possible to produce coatings having fluorine concentration gradients.
Where the nanoscale inorganic particulate solids are themselves prepared using one or more compounds which possess addition-polymerizable/polycondensable groups, there is no need for subsequent surface modification (although this is of course possible as an additional measure).
The variation in the nanoscale particles is generally accompanied by a variation in the refractive index and in the chemical resistance of the corresponding materials. For instance, the complete or partial replacement of SiO2 particles by ZrO2 and/or TiO2 particles leads to materials having higher refractive indices, the refractive index being, in accordance with the Lorenz-Lorentz equation, an additive product of the volume of the individual components. Replacing some or all of the SiO2 particles by boehmite, ZrO2 and/or TiO2 particles leads to materials of high alkali resistance.
The nanoscale inorganic particulate solids are used in the coating composition in, for example, an amount of from 0.20 to 2.00 mol per mol of component (a). Preferred amounts are in the range from 0.7 to 1.7 and in particular from 1.0 to 1.4 mol per mol of component (a).
It is also possible to add further hydrolysable compounds (e) of elements from the group consisting of Si, Ti, Zr, Al, B, Sn and V to the coating composition. They are preferably hydrolysed with the hydrolysable silane compounds of component (a). Compound (e) comprises a compound of Si, Ti, Zr, Al, B, Sn or V of the general formula RxM4+Rxe2x80x24-x or RxM3+Rxe2x80x23-x, where M is a) Si4+, Ti4+, Zr4+ or Sn4+ or b) Al3+, B3+ or (VO)3+, R is a hydrolysable radical, Rxe2x80x2 is a nonhydrolysable radical and x can be from 1 to 4 in the case of tetravalent metal atoms (case a) and from 1 to 3 in the case of trivalent metal atoms (case b). Where two or more radicals R and/or Rxe2x80x2 are present in one compound (e), they may each be identical or different. x is preferably greater than 1, i.e. the compound (e) has at least one, preferably two or more, hydrolysable radical(s).
Examples of the hydrolysable radicals are halogen (F, Cl, Br and I, especially Cl and Br), alkoxy (especially C1-4 alkoxy, such as methoxy, ethoxy, n-propoxy, xy, n-butoxy, isobutoxy, sec-butoxy or tert-butoxy), acyloxy (especially C1-4 acyloxy, such as acetoxy and propionyloxy). Particularly preferred hydrolysable radicals are alkoxy groups, especially methoxy and ethoxy.
Examples of nonhydrolysable radicals are alkyl groups (especially C1-4 alkyl such as methyl, ethyl, propyl and butyl) which may where appropriate contain one or more substituents such as halogen and alkoxy. Methacryloyl- and methacryloyloxypropyl-radicals may also be used in this context. As is evident, these compounds (e) (especially the silicon compounds) may also possess nonhydrolysable radicals which contain a Cxe2x80x94C double or triple bond.
Furthermore, the coating composition used in accordance with the invention may comprise customary additives, such as solvents, dissolved dyes, colour pigments, levelling agents, rheological additives, UV stabilizers and polymerization catalysts.
In order to set a simple mixing ratio and to adjust the rheological properties of the components it is possible where appropriate to add inert solvents after the lower alcohols have been distilled off. These solvents are preferably glycol ethers and alcohols which are liquid at room temperature. Particularly preferred solvents are C1-8 alcohols, especially 1-butanol, as low boilers, and glycol ethers, especially 1-butoxyethanol, as high boilers.
Application to the substrate is carried out by standard coating techniques such as, for example, dipping, spreading, brushing, knife coating, rolling, spraying, curtain coating and spin coating. It is preferred to apply a wet film of from 10 to 100 xcexcm, more preferably from 20 to 70 xcexcm and in particular from 30 to 50 xcexcm. The thickness of the crosslinked coat should be from 0.5 to 50 xcexcm, preferably from 1 to 20 xcexcm and in particular from 2 to 10 xcexcm. Self-crosslinking generally takes place at an ambient temperature of 20xc2x0 C. within 3 h to dryness state 5 and within 48 h to dryness state 6. If desired, of course, more rapid drying can be achieved by means of an increased temperature.
There is no restriction on the selection of the substrate materials for coating. The coating compositions are suitable with preference for coating wood, textiles, paper, stoneware, metals, glass, ceramics, plastics and alcohol-resistant organic paints, inks and plaster. The compositions are especially suitable for coating painted substrates, especially substrates with a 2K PU topcoat, metals or painted metal surfaces, and natural or artificial stone. Automobile body topcoats, building facades and facade elements in particular can be coated using the coating compositions obtained in accordance with the invention. Further fields of use include medical devices, medical engineering (dental material), outer surfaces of vehicles (also windscreens and mirrors), aircraft, motors and propellers, food preparation apparatus, milk production and processing, and pipes.
The articles coated in accordance with the invention acquire a permanent antiadhesive surface, and graffiti applied to this surface or posters stuck to it with paste are easy and simple to remove. It has been found that with the coating composition of the invention, especially when the abovementioned preferred proportions between the components are maintained, coatings are obtained which have good adhesion, abrasion resistance and scratch resistance and also water, oil and paint repellency properties. The self-crosslinking coats are colourlessly transparent, resistant to scratching, and possess a surface energy of less than 20 mJ/m2.
The coating composition may be obtained in particular by a method in which first of all two separate storable components (A) and (B) are prepared which then, by mixing, give the ready-to-apply coating composition. For ease of handling, the concentrations of the two components may be adjusted using one or more solvents so as to give, on mixing, simple (whole-number) mass proportions such as, for example, 3 parts (a) to 1 part (b). The pot life of the mixed components (A) and (B) is determined by the nature and proportion of the hydrolysable silane compounds of components a) and b) and of the amount of solvent used, and is preferably from 1.5 to 5 h.
The hydrolysable silanes of components a) to c) may be used as monomers or in partly condensed form. In one preferred embodiment one of components a) and b), preferably component a), is used with the fluorosilane in cocondensed form. In one preferred embodiment component (A) of the two-component coating system comprises such a cocondensate. For this purpose the fluorosilane is preferably added to the prehydrolysate of the silicon compound of component a) and cohydrolysed. This approach leads to coatings having a strong accumulation of the fluorosilane at the coat surface (strong fluorine gradient). In order to set a lower fluorine gradient, the fluorosilane may also be prehydrolysed separately or together with the hydrolysable compounds (e) or 10% by weight of the particulate material (d) and then added to the prehydrolysate of the silicon compound (a). Where the fluorosilane is of limited solubility in the prehydrolysate of component a), alcohols can be added as solubilizers. The reaction mixture is stirred thoroughly at room temperature until the added fluorosilane has been hydrolysed.
The examples which follow illustrate the invention.